NAND flash memory, as well as other types of non-volatile memories (“NVMs”), are commonly used in electronic devices for mass storage. For example, consumer electronics such as portable media players often include flash memory to store music, videos, and other media.
Conventional NVMs may include arrays of memory cells composed of floating gate transistors. To increase the storage capacity of a NVM while maintaining a small NVM size, some NVMs may store multiple bits of data in each memory cell. Such memory cells are commonly referred to as “multi-level cells” (“MLCs”). For example, a multi-level memory cell that is capable of storing 2 bits of data (e.g., a 2-bit memory cell) can include both a lower page and an upper page.
A multi-level cell can be programmed in stages. For example, for a 2-bit memory cell, the lower page of the memory cell can be programmed first. Once the lower page has been programmed, the upper page of the memory cell can be programmed. In addition, in order to read a programmed 2-bit memory cell, each of the lower and upper pages can be read separately.
Sometimes, however, a power loss event may interrupt the programming of a memory cell. For example, a power loss event can occur after the lower page of a memory cell has been programmed, but before the upper page of the memory cell has been fully programmed. This may result in an improperly programmed upper page.
When power is later restored, a system may attempt to read data from the memory cell. Conventionally, a state bit can be used to keep track of the last programmed memory cell, which can allow the system to handle the memory cell as an erased memory cell. In some situations, however, the value of the state bit can become unreliable, thereby causing the system to inadvertently use corrupted data obtained from an upper page of the memory cell. As used herein, “corrupted data” can refer to data obtained from a memory location of a NVM that is actually data stored in a different memory location of the NVM (e.g., lower page data obtained from an upper page of the memory cell).